The present invention relates to a palladium catalyzed method for making aromatic organic carbonates by the direct carbonylation of an aromatic organic hydroxy compound, such as phenol. More particularly, the present invention relates to a method for making aromatic organic carbonates using recycled carbonylation catalyst present in the carbonylation reaction mother liquor after recovery therefrom of a 1:1 molar adduct of the aromatic organic carbonate and aromatic organic hydroxy compound.
Aromatic organic carbonates, such as diphenyl carbonate are of interest to thermoplastic manufacturers, since they offer an alternative non-phosgene route to aromatic organic polycarbonates by melt transesterification. A procedure for making aromatic organic carbonates using an organic solvent, such as methylene chloride, is shown by Chalk, U.S. Pat. No. 4,187,242. Additional procedures for making aromatic organic carbonates are shown by Hallgren, U.S. Pat. Nos. 4,361,519 and 4,410,464, utilizing a molecular sieve as a drying agent for the water formed during the reaction. A further procedure for making aromatic organic carbonates by catalytic carbonylation of aromatic organic hydroxy compounds is shown by Japanese patent 01,165,551. Reference also is made to EP A89111581.8, utilizing a divalent or trivalent manganese salt or cobalt (II) salt in combination with hydroquinone and a palladium catalyst to catalyze the conversion of an aromatic organic hydroxy compound to an aromatic organic carbonate.
Prior to the present invention, as shown in copending application Ser. No. 07/906,681, filed Jul. 7, 1992, some aromatic organo carbonates were made by the carbonylation of an aromatic organic hydroxy compound, such as phenol, with a mixture of carbon monoxide and oxygen which were introduced into a reactor under constant composition gas flow conditions to substantially maintain the gaseous components at a constant molar ratio and partial pressure during the course of the reaction. Although the procedure of 07/906,681 for making aromatic organic carbonates provides improved yields, the effectiveness of the transition metal catalyst, for example, the combination of a divalent or trivalent manganese salt, or cobalt (II) salt, and hydroquinone and a palladium catalyst can be substantially impaired whenever an attempt is made to introduce make-up aromatic organic hydroxy compound into the reactor under ambient conditions. It would be desirable therefore to be able to make aromatic organic carbonates, by the direct carbonylation of aromatic organic hydroxy compounds, such as phenol using constant composition gas flow conditions, by providing recyclable transition metal catalyst to allow the introduction of make-up aromatic organic hydroxy compound, such as phenol into the reactor under ambient conditions.